1. Field of the Invention
The present invention relates to a semiconductor device capable of transmitting an electrical signal between two circuits having input electrical signals differing in potential from each other.
2. Description of the Related Art
In a case where an electrical signal is transmitted between two circuits having input electrical signals differing in potential from each other, a photocoupler is ordinarily used. The photocoupler has a light emitting element such as a light emitting diode and a light receiving element such as a phototransistor. An electrical signal input to the photocoupler is converted into light by the light emitting element and the electrical signal is restored from this light by the light receiving element, thus transmitting the electrical signal.
Since the photocoupler has the light emitting element and the light receiving element, it is difficult to reduce the size of the photocoupler. Also, the photocoupler is incapable of following an electrical signal if the frequency of the electrical signal is high. As a technique to solve these problems, a technique of transmitting an electrical signal by using inductive coupling between two inductors, for example, as described in National Publication of International Patent Application No. 2001-513276 has been developed.
Japanese Patent Laid-Open No. 10-163422 discloses a technique of forming an inductance by using a plurality of wiring layers stacked on a semiconductor substrate with interlayer insulating films interposed therebetween. In this technique, first circular-arc wiring patterns forming a winding on the input side and second-circular arc wiring patterns forming a winding on the output side are alternately stacked. In each wiring layer, one of the circular-arc wiring patterns is formed.
The present inventor has recognized as follows. With respect to reducing the size of a device which transmits an electrical signal between two circuits having input electrical signals differing in potential from each other, application of a semiconductor device manufacturing technique to forming inductors in two wiring layers so that the inductors face each other through an interlayer insulating film is conceivable. In such a case, the insulation withstand voltage between the two inductors is insufficient with respect to the potential difference between the two inductors due to the interlayer insulating film having a small thickness. There is, therefore, a demand for a technique to improve the insulating withstand voltage between the two inductors.